The present invention relates to an endermic medicament, i.e. a medicament for external application, with a gel base or carrier which is stable and has little interaction with the therapeutically effective ingredients contained in the medicament.
Several types of base materials for endermic medicaments are known including those for oil-base ointments, those for emulsions and those for water-soluble medicaments. As a trend in recent years, water-soluble medicaments having a gel-like consistency are highlighted by virtue of the high transparency to give a feeling of cleanness to the patients, good spreadability on the human skin, excellent percutaneous absorptivity of the therapeutically effective ingredients contained therein, easiness of removal by washing with water and other features. Several types of the gel base for such a water-soluble medicaments are already known and available on the market including carboxyvinyl polymers exhibiting excellent effects of thickening and gelation.
The above mentioned carboxyvinyl polymer is indeed an excellent gel base having high transparency to formulate an endermic medicament capable of giving satisfactory feeling of use to the patients. The polymer, however, has several problems caused by the fact that the polymer is basically a polymeric electrolyte.
The first problem in the polymer of this type is the possible interaction thereof with the therapeutically effective ingredients contained in the medicament due to the presence of the carboxyl groups in the polymer. When a gelled medicament with a basic compound as the effective ingredient is prepared with a carboxyvinyl polymer as the gel base, for example, a salt is sometimes formed between the effective ingredient and the polymeric base resulting in eventual coloration or formation of precipitates and decrease in the releasability of the effective ingredient for percutaneous absorption. On the other hand, furthermore, the gel medicament can be highly thickened only by the combined use of a basic compound for neutralization while some of basic compounds may have reactivity with the effective ingredient to cause coloration or precipitation. When the effective ingredient is ionic in the form of a salt, in addition, extensive and time-consuming investigations must be undertaken for each of the effective ingredients on the types and amounts of the basic compound for neutralization in order to obtain optimum consistency of the particular gel medicament sometimes leading to a conclusion that the amount of the basic compound for neutralization must be very large. Such a large amount of a basic compound of course has a detrimental effect against the healthy condition of the human skin to which the gel medicament is applied. Thus, carboxyvinyl polymers are under strict limitations as a gel base of endermic medicaments in respect of the formulation of the effective ingredients.